1. Field of the Invention
This invention relates to a process for making spandex by melt-spinning of polyurethaneureas and, more particularly, to a process of prepurifying the capped glycol prior to the formation of the polyurethaneurea.
2. Discussion of Background Art
Spandex has been traditionally prepared by reacting a polymeric glycol with a diisocyanate to form a capped glycol (an isocyanate-terminated prepolymer which contains a distribution of reaction products including unreacted diisocyanate), dissolving the capped glycol in a suitable solvent, contacting the solution with a diamine chain extender and optionally a monoamine chain terminator to form a solution of segmented elastomeric polyurethaneurea, and dry- or wet-spinning the solution to form spandex.
U.S. Pat. No. 3,415,790 discloses the preparation of spandex in which capped glycol is extracted before it is dissolved in a solvent, contacted with a difunctional chain extender, and dry-spun into filaments. In this method, polymer must be prepared and spun into fiber at the same site to avoid the expense of shipping solutions.
U.S. Pat. No. 3,503,933 discloses melt-spun spandex, but special, asymmetric diisocyanates are required which have at least a five-fold difference in the reactivity of the two isocyanate groups. Due to the presence of such diisocyanates, such spandex is expected to be unsatisfactory in processing (high tack and therefore difficult to backwind), in fabric properties (low unload power), and in fabric processing such as dyeing, finishing and laundering (high hot-wet creep).
Such methods are inadequate in that either a spinning solvent or special disocyanates are necessary to prepare the spandex, with resulting disadvantages in the spinning process or in the resulting spandex. A melt-spun process is still needed which will produce a spandex with good properties.